Anatectic origin of mid-Proterozoic granite dyke in the Isukasia area, West Greenland Pb-Pb and Rb-Sr isotope evidence

Abstract

It was found some time ago on the evidence of mineral-isotope relations that the early Archaean gneisses of the Godthåbsfjord region in West Greenland were mildly reheated during the mid-Proterozoic at c. 1600-1700 Ma (Pankhurst et al., 1973; Baadsgaard et al., 1976). A Rb-Sr whole-rock isotope study of a fine-grained granitic dyke from the Isukasia area indicated that this dyke was formed 1610 ± 130 Ma ago by anatexis of early Archaean rocks (Kalsbeek et al., 1980). This suggested that temperatures not less than c. 650°C were reached at depth, at least locally, within the Archaean craton during the Proterozoic. We have made a Pb-Pb isotope study of this dyke to check and amplify this conclusion. The field relations, petrology and chemistry of the dyke have been described in the earlier paper.